Conventional combustion meters typically employ a temperature sensor for monitoring the heat affect from the catalytic-heterogeneous combustion of fuels with excess oxygen. Most commonly used is the hot wire technique, which employs a resistance heated noble metal filament usually made of platinum. If filament is heated in an atmosphere containing fuels and sufficient oxygen for combustion, the combustion is catalyzed at the metal-interface. The heat release by the combustion raises the temperature of the wire filament thereby increasing the resistance. The wire filament typically serves as a branch in a bridge circuit. The conventional hot wire detector exhibits relatively low sensitivity which limits its usefulness for monitoring low fuel concentrations, i.e., less than 1%.
An improvement in the conventional hot wire detector can be realized through the use of commercially available thermistors. Commercially available thermistors however have suffered from the limited stability of the semiconductor material at high temperatures in an oxidizing environment, typically having a maximum operating temperature of 300.degree. C. This temperature is less than temperatures required for combustion of methane and other hydrocarbon fuels even in the presence of catalysts.
The following description in connection with the accompanying drawings describes a solid electrode electrochemical cell functioning as the combustibles sensor suitable for operation at a temperature range of about 500.degree. C to 1000.degree. C in the presence of oxidizing gases.